Abstract:

The next generation of nuclear safety analysis computer codes will include
detailed modeling of the interfacial area concentration. The interfacial area
concentration is the essence of the two-fluid model. It is the most accurate of the
two-phase models since it considers each phase independently and links the two
phases together with six conservation equations. The interfacial area concentration,
along with a driving potential, determines the energy, momentum and mass transfer
between the two phases.
The importance of this research lies in obtaining a greater understanding of the
developing nature of two-phase flows and the application of the two-fluid model.
With proper characterization of two-phase flow, the next generation of nuclear
safety analysis computer codes will be able to incorporate this information to
predict parameters during an accident scenario with greater precision. This research
will provide a first order look into the developing nature of two-phase flow.
As part of this research, the development of two-phase flow in a vertical
column was analyzed using double sensor impedance probes. The resident vapor
and liquid times were recorded along with the velocity of the vapor phase. By
creating distributions of the bubble residence times, liquid residence times,
velocities, and sizes, one can characterize the developing nature of the two-phase
flow. Data was taken at four different axial locations for six different flow rates.
The resulting data show clear trends in how the standard deviation and mean values
for the measured parameters change as a function of flow rate and axial position.
The void fraction contribution from the spherical/distorted bubble group as well as
the cap/slug bubble group was also recorded to determine the net transfer rate of
vapor between the two bubble groups. Interfacial area concentration was not
included in the measurement since the probes that were used can only determine
interfacial area concentration for spherical bubbles. Further research will be
conducted with the inclusion of interfacial area concentration at a later time.